1. Field of the Invention
The present invention relates to a liquid discharge head for applying a thermal energy to a liquid to generate a bubble and discharge the liquid, a liquid discharge method, and a liquid discharge apparatus.
Moreover, the present invention can be applied to apparatuses for performing recording on recording media such as paper, thread, fiber, cloth, leather, metal, plastic, glass, wood, ceramic, and the like, such as a printer, a copying machine, a facsimile machine provided with a communication system, and a word processor provided with a printer section, and further to an industrial recording apparatus combined with various processing apparatuses in a composite manner.
Additionally, xe2x80x9crecordingxe2x80x9d in the present invention means not only that a character image, a diagram image or another meaningful image is given to the recording medium, but also that a pattern image or another meaningless image is given.
2. Related Background Art
In conventional recording apparatuses such as a printer, an ink jet recording method, a so-called bubble jet recording method is known which comprises applying heat or another energy to a liquid ink in a flow path to generate a bubble, discharging the ink from a discharge port by an action force based on a steep volume change with the bubble, and attaching the ink to a recording medium to form an image. In a recording apparatus using the bubble jet recording method, as disclosed in U.S. Pat. No. 4,723,129 or the like, the discharge port for discharging the ink, the flow path connected to the discharge port, and an electrothermal converting element as energy generating means, disposed in the flow path, for discharging the ink are usually arranged.
According to the recording method, a high quality level image can be recorded with a high speed and a low noise, and the discharge ports for discharging the ink can be arranged with a high density in a head to perform the recording method, which provides many advantages that a high-resolution recorded image and further a color image can easily be obtained with a small-sized apparatus. Therefore, in recent years the bubble jet recording method has been utilized in many office apparatuses such as a printer, a copying machine, and a facsimile machine, and further in industrial systems such as a textile printing machine.
Various demands have been raised with utilization of such bubble jet technique in products of various fields, and for example, there are proposed drive conditions for providing a liquid discharge method to perform a satisfactory ink discharge with a fast ink discharge speed based on a stable bubble generation in order to obtain a high quality image, or improvement of a flow path configuration to obtain a liquid discharge head fast in refill speed of a discharged liquid into a liquid flow path from a viewpoint of high-speed recording.
Furthermore, in order to simultaneously achieve highly detailing of a recorded image and increasing of a printing speed, there is proposed a constitution in which a plurality of electrothermal converting elements are arranged in one liquid flow path (nozzle) and liquid droplets different in size are discharged from the same nozzle.
The discharge amount, discharge speed, refill frequency and other liquid discharge properties of the liquid discharge head are generally determined by three elements: (1) flow resistance before a heater (on a downstream side with respect to a flow direction of the liquid in the liquid flow path); (2) flow resistance behind the heater (on an upstream side); and (3) ratio of the flow resistance before the heater to the flow resistance behind the heater. Therefore, for the liquid discharge head, by adjusting a liquid flow path structure, heater size, arrangement position, and the like, the aforementioned three elements are appropriately changed, and a desired discharge property is obtained in the constitution.
In a liquid discharge head in which a plurality of electrothermal converting elements are arranged in one nozzle, and liquid droplets different in size are discharged from the same nozzle (hereinafter referred to also as xe2x80x9cdischarge amount modulation headxe2x80x9d), in order to realize highly detailing of a recorded image and accelerating of a printing speed, a discharge amount modulation ratio (volume ratio of a small liquid droplet to a large liquid droplet) needs to be increased.
When the discharge amount modulation ratio is increased, however, a discharge speed difference between the small and large liquid droplets increases and a deviation is generated in reaching (dot placement) position of the liquid droplet to a recording medium. Therefore, the small or large liquid droplet cannot be discharged within one scanning stroke, or it is necessary in some cases to change a discharge timing in accordance with a size of the liquid droplet to be discharged or to perform another high-grade image processing process. Moreover, when a size ratio of heaters disposed on one nozzle is increased, a nozzle length has to be increased, which deteriorates a refill frequency or exerts another large influence on a discharge property.
For the discharge amount modulation head, the discharge speeds of the respective liquid droplets are required to be substantially equal, while the discharge amount modulation head discharges different sizes of liquid droplets from the same nozzle, and it is difficult to optimize a nozzle structure for discharging the respective sizes of the liquid droplets. Moreover, since a plurality of heaters are arranged within one nozzle in the discharge amount modulation head, a heater size or a degree of freedom in arrangement position is limited in some cases.
As described above, in the discharge amount modulation head, much higher-grade condition is required concerning design than in a general liquid discharge head in which one heater is disposed in one nozzle. In a conventional art, in order to satisfy these conditions, a discharge efficiency is deteriorated and a head temperature easily rises, or it is necessary to increase dimensional precision or assembly precision of constituting components.
Therefore, an object of the present invention is to provide a liquid discharge head, liquid discharge method and liquid discharge apparatus in which a discharge amount ratio of liquid droplets can be increased, substantially equal discharge speeds of the respective liquid droplets can be provided, and a refill frequency after discharge can be raised.
To achieve the aforementioned objects, according to the present invention there is provided a liquid discharge head comprising: a discharge port for discharging a liquid; a liquid flow path whose one end portion constantly communicates with the discharge port and which comprises a plurality of bubble generating areas for generating a bubble in the liquid; a liquid supply port disposed in the liquid flow path and connected to a common liquid supply chamber for storing the liquid to be supplied to the liquid flow path; a plurality of bubble generating means, disposed in the liquid flow path, for generating the bubble in the liquid; and a plate-like movable member disposed in the liquid flow path with the side of the discharge port supported as a free end at a gap of 10 xcexcm or less with respect to the liquid supply port on the side of the liquid flow path, and provided with a projection area larger than an opening area of the liquid supply port. The discharge port is in a linear communication state with the bubble generating means, and by driving the bubble generating means for generating the bubble with a smallest volume among the plurality of bubble generating means, the movable member seals and substantially shuts off the liquid supply port.
Moreover, according to the present invention there is provided a liquid discharge head comprising: a discharge port for discharging a liquid; a liquid flow path whose one end portion constantly communicates with the discharge port and which comprises a plurality of bubble generating areas for generating a bubble in the liquid; a liquid supply port disposed in the liquid flow path and connected to a common liquid supply chamber for storing the liquid to be supplied to the liquid flow path; a plurality of bubble generating means, disposed in the liquid flow path, for generating the bubble in the liquid; and a plate-like movable member disposed in the liquid flow path with the side of the discharge port supported as a free end at a gap of 10 pm or less with respect to the liquid supply port on the side of the liquid flow path, and provided with a projection area larger than an opening area of the liquid supply port. The discharge port is in a linear communication state with the bubble generating means, and by selecting one of the plurality of bubble generating means, during generation of the bubble, and even during driving of any bubble generating means, the movable member seals and substantially shuts off the liquid supply port.
According to the liquid discharge head of the present invention constituted as described above, a part of the liquid filling the liquid flow path is heated by a heat generating member (bubble generating means), the movable member closely abuts on the peripheral portion of the liquid supply port to close the liquid supply port substantially simultaneously with occurrence of film boiling, and the inside of the liquid flow path is substantially in the sealed state excluding the discharge port.
Therefore, a pressure wave is inhibited from being propagated to the side of the liquid supply port, no liquid moves to the back of the heat generating member during discharge of the liquid, and a flow resistance behind the heat generating member is supposedly substantially infinite. Furthermore, since the flow resistance behind the heat generating member (on an upstream side) is substantially infinite, the ratio of the flow resistance before the heat generating member to the flow resistance behind the heat generating member constantly becomes substantially zero even with the change of the flow resistance before the heat generating member (on a downstream side). Therefore, for the liquid discharge head of the present invention, the liquid discharge property is determined only by the xe2x80x9cflow resistance before the heat generating member (on the downstream side)xe2x80x9d among three elements which determine the liquid discharge property.
The liquid discharge speed is inversely proportional to the flow resistance before the heat generating member, and is proportional to a bubbling power determined by an effective discharge area of the heat generating member. Moreover, since the discharge amount of the liquid discharged from the discharge port is proportional to the effective discharge area of the heat generating member, in the liquid discharge head of the present invention, by setting the ratios of the flow resistance before the respective heat generating members disposed in the same liquid flow path (on the downstream side) to the discharge amount to be equal, the discharge speeds of respective liquid droplets discharged by heating the respective heat generating members become equal. Thereby, according to the present invention, even when the liquid droplet discharge amount ratio is increased, it is easy to equalize the discharge speeds of the respective liquid droplets.
Moreover, the plurality of bubble generating means disposed in the liquid flow path are preferably arranged in order in which a bubbling area gradually increases toward the upstream side from the downstream side of the liquid flow path.
Furthermore, there may also be a gap between a liquid flow path wall constituting the liquid flow path and the movable member.
Moreover, the liquid may be discharged by driving the plurality of bubble generating means. In this case, the liquid may be discharged by simultaneously driving the plurality of bubble generating means. Moreover, the liquid may be discharged by first driving the bubble generating means closest to a discharge port side among the plurality of bubble generating means. Furthermore, the liquid may be discharged by first driving the bubble generating means closest to a movable member side among the plurality of bubble generating means.
Moreover, according to the present invention, there is provided a liquid discharge method using a liquid discharge head comprising: a discharge port for discharging a liquid; a liquid flow path whose one end portion constantly communicates with the discharge port and which comprises a plurality of bubble generating areas for generating a bubble in the liquid; a liquid supply port disposed in the liquid flow path and connected to a common liquid supply chamber for storing the liquid to be supplied to the liquid flow path; a plurality of bubble generating means, disposed in the liquid flow path, for generating the bubble in the liquid with which the liquid flow path is filled; and a movable member disposed in the liquid flow path with the side of the discharge port supported/fixed as a free end at a slight gap between a liquid flow path wall constituting the liquid flow path and the liquid supply port with respect to the liquid flow path wall and the liquid discharge port on the side of the liquid flow path, and provided with a projection area larger than an opening area of the liquid supply port. By driving the bubble generating means for generating the bubble with a smallest volume among the plurality of bubble generating means to generate the bubble, from when a drive voltage is applied to the bubble generating means until a period of substantially isotropic growth of the entire bubble ends, the movable member seals and substantially shuts off the liquid supply port.
Moreover, according to the present invention, there is provided a liquid discharge method using a liquid discharge head comprising: a discharge port for discharging a liquid; a liquid flow path whose one end portion constantly communicates with the discharge port and which comprises a plurality of bubble generating areas for generating a bubble in the liquid; a liquid supply port disposed in the liquid flow path and connected to a common liquid supply chamber for storing the liquid to be supplied to the liquid flow path; a plurality of bubble generating means, disposed in the liquid flow path, for generating the bubble in the liquid with which the liquid flow path is filled; and a movable member disposed in the liquid flow path with the side of the discharge port supported/fixed as a free end at a slight gap between a liquid flow path wall constituting the liquid flow path and the liquid supply port with respect to the liquid flow path wall and the liquid discharge port on the side of the liquid flow path, and provided with a projection area larger than an opening area of the liquid supply port. In a case of generating the bubble by selecting one of the plurality of bubble generating means, from when a drive voltage is applied to the bubble generating means until a period of substantially isotropic growth of the entire bubble ends, the movable member seals and substantially shuts off the liquid supply port even during driving any bubble generating means.
Thereby, the liquid flows into the liquid flow path before a retreat amount of a meniscus formed in the discharge port is maximized, and a flow for rapidly drawing the meniscus into the liquid flow path is rapidly reduced, so that the meniscus retreat amount decreases, and the meniscus starts to return to a position before bubbling at a relatively low speed. As a result, after the discharge, a time when the meniscus returns to its initial state is very short. Specifically, since a time for completing refilling of a constant amount of ink to the liquid flow path is very short, during performing of a high-precision (constant amount) ink discharge, even a discharge frequency (drive frequency) can rapidly be enhanced.
Furthermore, a bubble growth volume change and a time from bubble generation until bubble vanishing may largely differ between the discharge port side and the liquid supply port side in the bubble generating area in the constitution.
Additionally, the bubble generating area may not be opened to atmosphere in the constitution.
According to the present invention, there is provided a liquid discharge apparatus comprising: the liquid discharge head of the present invention; and drive signal supply means for supplying a drive signal for discharging a liquid from the liquid discharge head. Moreover, according to the present invention there is provided a liquid discharge apparatus comprising: the liquid discharge head of the present invention; and recording medium conveying means for conveying a recording medium to receive a liquid discharged from the liquid discharge head.
Furthermore, recording may be performed by discharging an ink from the liquid discharge head and attaching the ink to the recording medium in the constitution.
Other effects of the present invention will be understood from description of respective embodiments.
Additionally, xe2x80x9cupstreamxe2x80x9d and xe2x80x9cdownstreamxe2x80x9d for use in the description of the present invention are represented with respect to a flow direction of the liquid toward the discharge port from a liquid supply source via the bubble generating area (or the movable member), or with respect to a constitutional direction.
Moreover, xe2x80x9cdownstream sidexe2x80x9d regarding the bubble itself means the bubble generated on a downstream side of the flow direction or the constitutional direction with respect to a bubble center, or in an area on the downstream side from an area center of the heat generating member.
Furthermore, expression xe2x80x9cthe movable member seals and substantially shuts off the liquid supply portxe2x80x9d in the present invention includes a case in which the movable member does not necessarily closely abut on the peripheral portion of the liquid supply port, and limitlessly approaches the liquid supply port.